Fertilizers are materials which contain one or more nutrient elements essential for plant growth. Soil being the preponderant medium of plant growth, fertilizers are usually considered as soil amendments to alleviate natural deficiencies and/or to replace nutrients removed in cropping regimens. The bulk of plant tissue is comprised of carbon, hydrogen and oxygen. These elements are acquired from atmospheric carbon dioxide and soil water. Of the additional mineral elements found in plants, and obtained from the soil, twelve are presently considered essential.
The primary nutrients, utilized in large amounts and most likely to be limiting to plant growth, are nitrogen, phosphorus and potassium. The fertilizer industry has been built principally on supplying materials containing these primary nutrients, either singly or in combinations. Calcium, magnesium and sulfur are also used by plants in relatively large amounts, but on most soils are not as apt to be limiting, and hence are called secondary nutrients. Iron, copper, manganese, boron, zinc and molybdenum constitute the so-called minor or trace nutrients, essential to plant growth in minute amounts. Other elements are being scrutinized continuously for their influence on plants, and it is possible that the list of essential nutrients may be extended.
Materials which have been utilized to supply plant food elements may be classified broadly as: by-products and wastes of other industries; natural organics; natural minerals; refined minerals; and manufactured chemicals. Representatives of these classes are either applied directly to the soil as so-called separate materials or are used in various combinations in the manufacture of mixed fertilizers. Separate materials may supply more than one nutrient element, either primary, secondary or trace, whereas mixed goods always contain two or more primary nutrients and may contain other essential elements as well. The fertilizer industry of today is primarily a chemical industry, and plant food mixtures are produced from chemicals readily available to plants.
When it is desired to provide a fertilizer capable of dispensing sulfur, magnesium and potassium one has two choices. One choice comprises selecting any of the natural minerals containing sulfur, magnesium and potassium such as langbeinite or kainite. Langbeinite is found in the State of New Mexico, U.S.A., Germany and India but in its natural state it also contains sodium chloride so that before it can be used as an agricultural fertilizer it must be stripped of its sodium chloride. Langbeinite has the formula K.sub.2 SO.sub.4.2MgSO.sub.4. Another natural mineral which is available in kainite having the formula KCl.MgSO.sub.4.3H.sub.2 O and is mined for agricultural purposes. One advantage of these natural mixed salts is their stability in the presence of moisture so that once these products have been pelletized their stability to humid conditions makes them suitable for use in fertilizer dispensing machines without the production of appreciable amounts of fines which cause clogging problems to such dispensing equipment and without hydration which weakens the crystalline structure.
The other choice is to reproduce the elements of langbeinite or kainite by chemical mixture. It has been found that a mixture of potassium sulfate and magnesium sulfate to reproduce langbeinite cannot be pelletized unless some of the binding agents normally used in the art of making tablets or pellets are incorporated in the mixture. Also when attempting to reproduce kainite by mixing potassium chloride and trihydrated magnesium sulfate it has been found that though this mixture can be pelletized without the aid of binding agents, the compressed mixture or pellet when let standing in air absorbs too much humidity so that there is a substantial gain in weight of the pellet in the order of 12 to 25% with the end result that such a tablet or pellet does not possess sufficient strength to resist the handling by pellet-dispensing machines.
Furthermore since the availability of natural salts such as langbeinite and kainite is limited, and and since, in the case of langbeinite, the cost of transportation to North American markets would render this product less competitive in such markets it would thus appear that it would be highly desirable if these desired salts could be made locally in the absence of bining agents in such a manner as to be suitable for use in regular pellet-dispensing machines.